feat: add BreadcrumbProvider and e2e test suite

Add BreadcrumbProvider context so pages can override TopBar breadcrumbs
dynamically. Add Playwright e2e tests for dashboard, agents, routes,
exchanges, and admin pages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

playwright.config.ts

@@ -0,0 +1,21 @@
+import { defineConfig } from '@playwright/test'
+
+export default defineConfig({
+  testDir: './e2e',
+  timeout: 30_000,
+  retries: 0,
+  use: {
+    baseURL: 'http://localhost:5173',
+    headless: true,
+    viewport: { width: 1440, height: 900 },
+  },
+  projects: [
+    { name: 'chromium', use: { browserName: 'chromium' } },
+  ],
+  webServer: {
+    command: 'npm run dev',
+    port: 5173,
+    reuseExistingServer: true,
+    timeout: 15_000,
+  },
+})